[llvm-branch-commits] [llvm] [InstCombine] Improve inbounds preservation for ADD+GEP -> GEP+GEP (PR #135155)

[Nikita Popov via llvm-branch-commits]

================
@@ -3087,12 +3087,22 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
     return nullptr;
 
   if (GEP.getNumIndices() == 1) {
-    // We can only preserve inbounds if the original gep is inbounds, the add
-    // is nsw, and the add operands are non-negative.
-    auto CanPreserveInBounds = [&](bool AddIsNSW, Value *Idx1, Value *Idx2) {
+    auto CanPreserveNoWrapFlags = [&](bool AddIsNSW, bool AddIsNUW, Value *Idx1,
+                                      Value *Idx2) {
+      // Preserve "inbounds nuw" if the original gep is "inbounds nuw",
+      // and the add is "nuw".
+      if (GEP.isInBounds() && GEP.hasNoUnsignedWrap() && AddIsNUW)
+        return GEPNoWrapFlags::inBounds() | GEPNoWrapFlags::noUnsignedWrap();
----------------
nikic wrote:

```suggestion
      if (GEP.hasNoUnsignedWrap() && AddIsNUW)
        return GEP.getNoWrapFlags();
```
Would this work to subsume both this case and the only nuw one below?

https://github.com/llvm/llvm-project/pull/135155